Head-up display devices present data without requiring users to look away from their usual viewpoints. Head-up displays have historically seen extensive use in aircraft applications, and are now being utilized in application other than aircraft (e.g., automotive applications).
FIG. 1 shows angles of light when viewing a direct image. Light 102 from a pixel in a display 100 is collected by the eye lens within a user's eye 104 and is focused on the retina. The position of a pixel on the retina is determined by the angle of the light 102 of that pixel to the eye lens. The angle from a pixel to the eye lens depends on the distance from the display 100 to the eye 104 and its position within the image. Each pixel is characterized by a unique angle, and the eye sees the image at the real distance where the image is positioned.
FIG. 2 shows angles of light when viewing a virtual image. A virtual image identical to the real image of display 100 can be made using a smaller display 200 by imitating the angles of the real image at the eye lens using optics 202, 204. The entire image is presented to the eye as a collection of angles, where each pixel is represented by a unique angle. The eye sees a large image far away. The actual display 200 is smaller and much closer.
FIG. 3 shows a prior art head-up display that displays a virtual image. Head-up display (HUD) device 300 uses the techniques shown in FIG. 2 to present a large virtual image 302 to a vehicle operator 304. The image provided by HUD device 300 is reflected by the vehicle windshield into the vehicle operator's field of view, and presents the virtual image 302 focused at a distance d from the vehicle operator. The distance d is set by the optics and geometry of the system shown in FIG. 2.